Antarctic ice shelves are fed primarily by the glaciers flowing into them. Downstream
of promontories separating these glaciers, super-cooled water can rise and freeze into
suture zones, leading to the accretion of marine ice. Marine ice bodies have been found
in several Antarctic ice shelves, but little is known about their detailed geometry, rate of
accretion, or influence on ice dynamics. In this study we investigate marine ice in a
suture zone downstream of the Joerg Peninsula in the southern part of the Larsen C Ice
Shelf, Antarctic Peninsula. We present ground penetrating radar data from which we
infer the boundaries between the meteoric and marine ice bodies and, in combination
with GPS data and assuming hydrostatic equilibrium, estimate marine ice thickness
within a suture zone. We show that the Joerg Peninsula suture zone contains marine ice
layer, which is increasing in thickness along-flow from ~140 m to 180 m over 20 km,
implying an average basal accretion rate of ~0.5 m a-1 in our study area. We examined
the impact of this marine ice on ice shelf dynamics by modeling the suture zone within
an ice flow model. The results, which replicate observed surface velocities and strain
rates, show that the warmer and thus softer ice of the suture zone serves to channel
shear deformation. This enables decoupling of neighboring flow units with different
follow velocities, while maintaining the structural integrity of the ice shelf.